It is known that electric batteries of the accumulator type, particularly lead batteries, are constituted by mutually connected cells or accumulators, each of which is composed of at least one pair of plates, an anode and a cathode, immersed in electrolyte. Separators, generally constituted by thin diaphragms, are usually inserted between the positive and negative plates in order to prevent plates of opposite polarities from coming into mutual contact.
Said batteries are built by using containment enclosures that can be closed with appropriate lids; the entire assembly is made of high-strength plastics in order to minimize, barring exceptionally forceful impacts, the possibility of cracking or breakage, also due to internal overpressure.
The most widely used plastic materials are propylene-ethylene copolymers, such as polypropylene, which has excellent mechanical strength, satisfactory behavior with respect to temperature variations and to the action of acids, solvents, oils, et cetera, and can be heat-sealed.
Other plastic materials that have these properties can of course be used to manufacture containment enclosures or containers.
The structure of such battery containers is of the monolithic type, obtained usually by molding and with generally standardized external shapes, having a rectangular or square cross-section.
The monolithic part is divided internally into compartments that form the cells suitable to contain the groups of plates, their supports and the corresponding electrolyte.
The plate is the unit that on its own, or combined with other identical plates, constitutes one of the electrodes. Each plate is identically formed by a supporting grid and by the active material that is the main solid component, in which the electrochemical reactions, on which the operation of the battery is based, take place.
The battery element is formed by a set of positive and negative plates with separators interposed, said plates being welded to each other in a parallel configuration by means of a bridge, multiple elements being then interconnected in series by way of connectors.
Such elements or packs of plates, which can have variable thicknesses or widths, are inserted, preferably wrapped in respective plastic bags, and are accommodated in the respective containment cells of the monolithic part.
Since the plates are constituted by grids made of lead-based alloys, which are rather soft and heavy, and onto which the active material is applied, they are particularly sensitive to mechanical stresses such as impacts, compressions, friction, shearing or vibration.
It is therefore very important to insert the packs of plates, during assembly of the battery, as nontraumatically as possible and to fix them in position against movements and vibration once they have been inserted in their respective cells.
Containers are known which have various systems for keeping the plates in position, such as protrusions or locking elements, inserted in the cells. Said plates must have dimensions that allow to insert them with limited play between the walls of the cells in order to prevent any movement thereof.
In any case, the plates must be inserted very carefully and by highly skilled individuals, since the guiding or locking protrusions of the plates have edges that easily tear the wrappers of the plates or even the plates themselves.
These problems have been partially solved in the known art by providing resilient elements for supporting or locking the plates, such as saddles (see EP-A-543416) or pads for horizontally stacked plates (see U.S. Pat. No. 4,603,093) or also tear-resistant reinforced wrappers for said plates (see U.S. Pat. No. 4,663,253 or U.S. Pat. No. 4,788,113).
Since containers and/or plates are currently often manufactured by different manufacturers, and are possibly assembled by yet another battery manufacturer, even small size variations of the plates sometimes make their insertion and fixing in the corresponding containers impossible or defective.
Furthermore, it is known that during the active life of the battery, the grids, especially the positive ones, may increase in size, particularly due to corrosion processes.